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Precise estimates of protostellar masses are crucial to characterize theformation of stars of low masses down to brown-dwarfs (BDs; M* < 0.08 Msun).The most accurate estimation of protostellar mass uses the Keplerian rotationin the circumstellar disk around the protostar. To apply the Keplerian rotationmethod to a protostar at the low-mass end, we have observed the Class 0protostar IRAS 16253-2429 using the Atacama Large Millimeter/submillimeterArray (ALMA) in the 1.3 mm continuum at an angular resolution of 0.07" (10 au),and in the 12CO, C18O, 13CO (J=2-1), and SO (J_N = 6_5-5_4) molecular lines, aspart of the ALMA Large Program Early Planet Formation in Embedded Disks(eDisk). The continuum emission traces a non-axisymmetric, disk-like structureperpendicular to the associated 12CO outflow. The position-velocity (PV)diagrams in the C18O and 13CO lines can be interpreted as infalling androtating motions. In contrast, the PV diagram along the major axis of thedisk-like structure in the 12CO line allows us to identify Keplerian rotation.The central stellar mass and the disk radius are estimated to be ~0.12-0.17Msun and ~13-19 au, respectively. The SO line suggests the existence of anaccretion shock at a ring (r~28 au) surrounding the disk and a streamer fromthe eastern side of the envelope. IRAS 16253-2429 is not a proto-BD but has acentral stellar mass close to the BD mass regime, and our results provide atypical picture of such very low-mass protostars.

Early Planet Formation in Embedded Disks (eDisk) VI: Kinematic Structures around the Very Low Mass Protostar IRAS 16253-2429